Govt. Exams
Entrance Exams
ADH binds to V2 receptors on collecting duct cells, triggering cAMP production that moves aquaporin-2 water channels to the apical membrane, increasing water permeability.
High-frequency stimulation causes calcium to accumulate in the sarcoplasm faster than it can be reuptaken by SR, maintaining sustained actin-myosin interactions.
SSRIs block serotonin reuptake transporters, preventing reabsorption of serotonin from the synaptic cleft and increasing its availability for receptor binding.
pH homeostasis involves buffer systems (bicarbonate, phosphate, proteins), respiratory control of CO2, and renal regulation of H+ and HCO3- ions.
While more RBCs carry oxygen, increased blood viscosity decreases flow rate, potentially reducing net oxygen delivery. The optimal hematocrit is around 45% for maximum oxygen transport.
CFTR chloride channels regulate fluid secretion in mucus-producing tissues. Defective CFTR impairs Cl- secretion, causing secondary reduced water secretion and excessive Na+ reabsorption, producing thick, viscous mucus that obstructs respiratory airways.
The Bohr effect is multifactorial: decreased pH (lactate, CO2), increased PCO2, increased temperature, and elevated 2,3-BPG all decrease hemoglobin's O2 affinity, promoting oxygen unloading precisely where metabolic demand is highest.
Decreased GFR reduces NaCl delivery to the macula densa in the thick ascending limb. This chemoreceptor senses decreased NaCl uptake and signals JG cells to reduce renin secretion, allowing afferent arteriolar vasodilation to restore GFR.
Factor VIII is a critical cofactor in the intrinsic coagulation pathway (Factor VIII-von Willebrand complex). Its deficiency specifically impairs activation of Factor X, prolonging aPTT while PT remains normal.
Glucose is actively reabsorbed via Na-glucose cotransporter (SGLT1) at the apical membrane using Na+ gradient, then exits via facilitated diffusion (GLUT2). Water follows osmotically via aquaporins, maintaining osmotic balance.
